Who is the RAB?

[Andrew]

No: HPFGUIDX 137099

I do not know if this has been posted, I attempted a search but the 
many posts instantly put a stop to that. The first name to come to 
mind on reading about RAB in HBP was of Regalus Black. R*B... All that 
we need to know is his middle name; I find this name the most likely 
as it would tie in with Sirius.

Perhaps we could simply start a list and if anyone has a name that 
they would like to add they can put it here, and their comments below. 
We could then take time to argue them in turn.

Regalus Black